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+/*
+ * Copyright (C) 2020 Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * This class is used to control the document focus when a non-body element contains the main scrollbar.
+ * Web browsers will not automatically focus a custom element with the scrollbar on load, which results in
+ * keyboard shortcuts (e.g. arrow keys) not controlling page scroll. Instead, this class will manually
+ * focus a dummy element inside the main content, which gives keyboard scroll focus to that element.
+ */
+class DocumentFocusController {
+ constructor() {
+ this._contentScrollFocusElement = document.querySelector('#content-scroll-focus');
+ }
+
+ prepare() {
+ window.addEventListener('focus', this._onWindowFocus.bind(this), false);
+ this._updateFocusedElement(false);
+ }
+
+ blurElement(element) {
+ if (document.activeElement !== element) { return; }
+ element.blur();
+ this._updateFocusedElement(false);
+ }
+
+ // Private
+
+ _onWindowFocus() {
+ this._updateFocusedElement(false);
+ }
+
+ _updateFocusedElement(force) {
+ const target = this._contentScrollFocusElement;
+ if (target === null) { return; }
+
+ const {activeElement} = document;
+ if (
+ force ||
+ activeElement === null ||
+ activeElement === document.documentElement ||
+ activeElement === document.body
+ ) {
+ // Get selection
+ const selection = window.getSelection();
+ const selectionRanges1 = this._getSelectionRanges(selection);
+
+ // Note: This function will cause any selected text to be deselected on Firefox.
+ target.focus({preventScroll: true});
+
+ // Restore selection
+ const selectionRanges2 = this._getSelectionRanges(selection);
+ if (!this._areRangesSame(selectionRanges1, selectionRanges2)) {
+ this._setSelectionRanges(selection, selectionRanges1);
+ }
+ }
+ }
+
+ _getSelectionRanges(selection) {
+ const ranges = [];
+ for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
+ ranges.push(selection.getRangeAt(i));
+ }
+ return ranges;
+ }
+
+ _setSelectionRanges(selection, ranges) {
+ selection.removeAllRanges();
+ for (const range of ranges) {
+ selection.addRange(range);
+ }
+ }
+
+ _areRangesSame(ranges1, ranges2) {
+ const ii = ranges1.length;
+ if (ii !== ranges2.length) {
+ return false;
+ }
+
+ for (let i = 0; i < ii; ++i) {
+ const range1 = ranges1[i];
+ const range2 = ranges2[i];
+ try {
+ if (
+ range1.compareBoundaryPoints(Range.START_TO_START, range2) !== 0 ||
+ range1.compareBoundaryPoints(Range.END_TO_END, range2) !== 0
+ ) {
+ return false;
+ }
+ } catch (e) {
+ return false;
+ }
+ }
+
+ return true;
+ }
+}